Having attained final technical approval from ISO on September 4, C++ 20 is expected to be formally published toward the end of this year, introducing new features such as modules and coroutines.
Designed in 1979 for systems programming, C++ remains a vital language. C++ was even found to be the fastest-growing language in the Tiobe Index of September 2020, where it ranks in fourth place behind C, Java, and Python. Tiobe cites the C++ 20 specification as one of the factors giving the language a boost.
New capabilities in C++ 20 include:
- Modules, enabling programmers to use modular components.
- Concepts, used to specify template requirements and support generic programming. Concepts promise to improve code quality.
- A synchronization library, for better support of fine-grained hardware control.
- Compile-time computation improvements.
- Coroutines, which generalize subroutines for use in nonpreemptive multi-tasking. Standardized support for coroutines in the standard library is still lacking, however. This support is eyed for C++ 23.
- Ranges, which provide components to deal with ranges of elements.
- Feature test macros, a set of macros that correspond to language and library features from C++ 11 or later.
- Precalculated hash values in lookup.
- Expansion statements to enable compile-time repetition of a statement for each element of a tuple, array, class, parameter pack, or range.
- Monadic operations for
std::optionalcode. - Implicit creation of objects for low-level manipulation.
- Improved context-sensitive recognition of
importandmoduleto aid non-compiler tools to determine build dependencies. - New rangified algorithms.
A contracts capability that had been expected in C++ 20, to specify pre-conditions, post-conditions, and assertions, has been removed. Contracts is now marked as a C++ 23 item, although it may not make it into that release, either.